In an electromagnetic device, such as an electromagnetic actuator of an electronic valve timing system for a motor vehicle, it is often necessary to join a "soft" magnetic material and a hardened, non-magnetic or magnetic material. Typically, the soft magnetic material is in the form of an armature and is annealed to remove most internal stresses and any carbon which may be within the material. The annealing process accounts for consistent magnetic and mechanical performance characteristics of the magnetic circuit components. In an actuator, the hardened material is in the form of a shaft.
One approach to joining the shaft to the armature is to use a brazing technique. However, this process requires high temperature which may destroy the magnetic properties of the armature. Further, the cool down rate may affect the hardness of the shaft and/or the magnetic properties of the armature.
Accordingly, a there is a need to join a soft magnetic material to a hardened material so as to maintain the hardness of the shaft and the magnetic properties of the armature.